The present invention relates to a refrigerant circuit of a refrigerating apparatus using a non-azeotropic refrigerant and to refrigerant circuit control.
FIG. 15 is a conventional refrigerating apparatus in which a non-azeotropic refrigerant is used and which is disclosed in, for instance, Japanese Patent Application. Laid-Open No. 75280/1996. This refrigerating apparatus is provided with a refrigerating circuit in which a compressor 1, a condenser 3, a first capillary tube 4, an evaporator 5, and an accumulator 6 are sequentially connected in loop form by the piping and in which a non-azeotropic refrigerant circulates; a bypass pipe 8 which bypasses the refrigerant circuit from the pipe between the compressor 1 and the condenser 3 to the pipe between the compressor and the evaporator and in which a cooling means 9 and a second capillary tube 10 are connected; a temperature detector 12 and a pressure detector 13 for detecting the temperature and pressure of an outlet portion of the second capillary tube; and a composition calculator 14 for calculating the composition of the refrigerant circulating in the refrigerant circuit. The composition of the refrigerant circulating in the refrigerant circuit can be calculated in this refrigerating apparatus, and the operation of the refrigerating apparatus is controlled on the basis of this composition of the refrigerant.
With the conventional technology, however, there has been no method for maintaining the condensing temperature and the evaporating temperature to fixed levels as a means for appropriately controlling the operation of the refrigerating apparatus using a non-azeotropic refrigerant. Namely, since the condensing temperature and the evaporating temperature have been determined with the cyclic composition fixed or with the cyclic composition fixed for each operating condition, it has been impossible to follow up, or sufficiently follow up, changes in the condensing temperature and evaporating temperature with respect to changes in the cyclic composition. In addition, it has been impossible to demonstrate a predetermined capacity at the time of gas leakage or erroneous charging of the refrigerant.
Further, with the refrigerating apparatus using a non-azeotropic refrigerant, if the cyclic composition of the refrigerant changes, the condensing pressure and the evaporating pressure change in a case where the condensing temperature and the evaporating temperature change. For this reason, the flow rate of the refrigerant circuit changes, so that it is impossible to secure a stable capacity, and it is difficult to secure subcooling on the inlet side of a throttling device. Namely, there has been a problem in compatibility in the securing of subcooling and the securing of the refrigerant flow rate.
Further, with the refrigerating apparatus using a non-azeotropic refrigerant as well, in the operation at a low outdoor air temperature, since the refrigerant which left the compressor becomes condensed in the refrigerant pipe where the refrigerant is cooled, the amount of refrigerant supplied to the compressor temporarily becomes smaller than the amount of refrigerant which leaves the compressor, with the result that the pressure within the suction portion of the compressor declines, leading to the malfunction of the compressor.
Further, since the pressure is higher for R.407C than R.22 at the same temperature, the malfunction of the refrigerating apparatus due to an excess rise in the pressure at the discharge portion of the compressor has been more liable to occur in the case of the refrigerating apparatus using R.407C than in the case of the refrigerating apparatus using R.22.
In addition, with refrigerant R.407C, the malfunction of the compressor due to corona discharge under vacuum has been more liable to occur than refrigerant R.22.
In addition, with the refrigerating apparatus using refrigerant R.407C and ester oil and ether oil which are refrigerating machine oils used for R.407, sludges which adversely affect the refrigerating apparatus have been liable to occur in large amounts.
In addition, with the non-azeotropic refrigerant, it has been impossible to accurately detect the compression of the refrigerant in the compressor, with the result that a malfunction has been liable to occur in the compressor.
In addition, with the non-azeotropic refrigerant, it has been impossible to accurately detect the excessive superheating of the compressor on the discharge side of the compressor.
In addition, with the non-azeotropic refrigerant, it has been impossible to accurately detect a decline in the concentration of the lubricating oil in the compressor due to excessive supply of liquid refrigerant.
In addition, with the non-azeotropic refrigerant, it has been difficult to obtain subcooling at the condenser outlet.